Loading coil



April l0, 1951 E. J. CRANE Er A1.

LOADING COIL 2 Sheets-Sheet 1 Filed Dec. 20, 1946 pll l0 1951 E. J. CRANE ET AL 2,548,199

LOADING COIL 2 SheeCS-Sheet 2 Filed Dec. 20, 1946 Patented pr. l0, 195i LOADING con.

vEdward J. Crane, Oak Park, and Robert P. Cross, Jr., Riverside, Ill., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application December 20, 1946, Serial No. 717,526

4 Claims.

This invention relates to inductively loaded transmission lines and more particularly to loading coil assemblies for use in communication transmission lines.

Telephone lines ordinarily run in pairs which are often encased with a plurality of other pairs in a sheathed cable, for example, lead covered cable. In order to load the lines, the cable is cut and loading coils are connectedin series with each line requiring inductance loading. vThe loading coils themselves are usually grouped in a case which is either suspended from the cable or fromv a, pole adjacent to the point at which the loading coils are spliced into the cable. The type of loading coil heretofore used required relatively cumbersome cases in which the required number of loading coils were disposed. Also, whenever it was necessary to load the cable heretofore, line connections had to be made to extend from the cable into the loading coil case.

An object of this invention is to provide a new and efficient loading assembly for telephone lines and a method of making the same.

In accordance with one embodiment of this invention, telephone lines in a cable may beinductively loaded by connecting into the lines one or more dowel-mounted loading coil assemblies,

each of said assemblies comprising one or more toroidal coils mounted on a dowel and each having associated therewith a terminal support of the type described and claimed in the co-pending application, E. L. Drom, case l, Serial No. 717,527 led December 20, 1946. Each of said assemblies is'varnish impregnated to protect it from adverse atmospheric conditions. When a plurality of lines are to be loaded, the entire loading unit may be made very compact by careful consideration in the design with respect to the number of coils mounted on each dowel and the number of dowel-mounted assemblies placed structurally in parallel. Such a complete loading complement may be spliced into and sheathed in the same cable with only a slight bulge in the cable, thereby eliminating a separate depending loading unit.

A complete understanding of the invention ,may be had by reference to the following detailed description taken nconjunction with the accompanying drawings, in which Fig. l is an overall illustration of one embodiment of the invention showing a loading coil assembly with parts broken away to show more clearly the relationship of the component parts of the assembly;

Fig. 2y is a cross-sectional view of the device shown in Fig. l taken on the line 2-2 of Fig. 1;

Fig. 3 is a cross-sectional view of the device shownv in Fig. 1 taken on the line 3-3 of Fig. l with the coating omitted to show more clearly the manner in which a terminal supporting washer is connected;

Fig. 4 is a cross section of a device in Fig. 1 taken along the line 4-4 of Fig. 1 with the coating omitted and shows the next consecutive terminal Washer-from that shown in Fig. 3 and illustrates thev staggering of the adjacent coils and the reversal of alternate terminal supporting washers;

Fig."5 is a view partly in cross section and partly in elevation showing a group of loading coil assemblies connected into a relatively large cable with a sleeve surrounding the loading units and extending to and over the ends of the cable covering; Y

" Fig. 6 is a cross-sectional view of the apparatus shown in Fig. 5 taken on the line 6 6 of Fig. 5;

Fig. '7 illustrates one loading coil assembly; and Fig; 8is Va cross section of the loaded cable shown in Fig. I taken on the line 8-8 of Fig. '7. As will be'seen in the drawings, a loading coil assembly I9 may comprise a plurality of similar toroidal coils 28, -mounted on a dowel 2! and `Washer is an ironl washer 23 which provides shielding to prevent cross talk. Associated with each coil is a terminal supporting washer 32 having insulated wires 33, 34, 35, and 3B embedded therein and extending therefrom. One end of each of said wires is cut short to form terminal stubs 4U, 4I, 42 and 43 to which the ends of the windings of the coils are electrically connected and the other ends of the wires 44 are relatively long so that they may be connected to the individual wires ofthe cable. The terminal supporting washer 32 isl of the type described and claimed in the co-pending application of E. L. Drom, case 1, Serial No. 717,527, led December 20, 1946. Any desired number of such coils maybe mounted on the dowel 2l after which the windings on thecoils are connectedl to their respective stub terminals on the terminal Washers. To aid in reducing cross-talliand other objectionable inductive effects between adjacent coils, their angular displacement around the rod may be staggered as illustrated in the drawings (Figs. 3 and 4) by rotating the position of every other coil. Fig. 3 clearly shows one coil and its associated terminal supporting washer and Fig. 4 shows the coil adjacent to the coil shown in Fig. 3. A comparison of these figures illustrates the relative angular displacement between two adjacent coils. As an aid in staggering the positions ci the coils every other terminal washer 32 may be turned over as shown inFigs. 3 and 4. IThe coils are held rmly on the dowel by fasteners, for example, spring fastening washers l5 forced over the dowel ends and againstl the iron washers at both ends. v

After the coils have been assembled 4on the dowel rods 2l, strips of tape 46 and 4l are secured on the peripheral Surfaces of the coils in the direction of the length of the dowel 2l and adjacent to the terminal stubs in order to prevent possible short circuits from being made between the terminal stubs and thecoil Windings during handling thereof.y After these tapes are applied, the stubs are bent over transversely of the length of the tape as shown in the drawings. Additional strips of tape lill are laid in the same direction over the terminal stubs which have previously been bent over. The long ends of the wires 44 leading from the terminal Washers v32 are brought out along the length of the loading coil assembly at both ends and are secured at the ends of the assembly byadditional tape 52 wrapped around each end of the assembly.

VAll the coil ends that are to be connected into one section of the cable should be connected to conductors brought out at one end of thek loading coil assembly and the other ends of the windings should be connected to kthe conductors brought out at the other end of the assembly. The entire assembly is thoroughly impregnated with an insulating compound, for example, varnish, to protect it from adverse atmospheric conditions. An excellent method of impregnating for this purpose is to subjectthe assembly to impregnation while under a vacuum. u

Before impregnating it is advisableto dry the coil assembly by placingeit in a closed tank, reducing the pressure to about :**millimeters of mercury and heating between 220 and V2.4.0" F. for about iour h-ours. The assembly may be cooled for about an hour in the -tank under a pressure of about 25 millimeters of mercury after which an impregnating compound, for example, a solvent-type varnish may be introduced into the tank until the coil assembly is immersed in the varnish where it should remain for about forty-'live minutes. The assembly may then be "air dried and drained for about an hour and then baked at from 265 to 275 F. for Y:from eight to ten hours. While still Warm from the baking, the coil assembly may be dash-dipped in the solvent-type insulating varnish for about ve minutes, then drained for about live minutes and then baked again as heretofore described.

After cooling for fromA two to four hours, the coil assembly may be coated by immersing it 'for about ten minutes in a mixture of solvent-type insulating varnish and a filler, for example, talc. The coil assembly may now be allowed to dryzfor a period of ve to six hours and then baked for about two hours at a temperature of 265" to 275 F. after which it may be cooledfor a period of about three to four hours. Another. coating may be applied in the same manner yas the last 4 described coating except that the iinal baking should take about ve hours. The solvent-type varnish heretofore referred to may be Harvell Varnish.

The loading coil assembly described herein may be used wherever loading is necessary, either at a splice point at the end of the normal length of the cable or at any other point of the cable by cutting the cable to permit the connection therein of the loading coil or coils. The assembly unit is so compact that it may be sheathed in with the rest of the cable at the point of insertion.

For example, as shown in Fig. 7, a telephone cable 53 comprising a plurality of telephone lines 54 surrounded by a lead sheath 55 may be inductively loaded by removing as much of the lead sheath as is necessary and connecting the coils of a loading coil assembly to the particular lines 56 that require inductive loading. Those telephone lines 60 that do not have to be loaded may pass intact along side the loading unit and the entire open section 'of the cable together with the loading unit may be covered by a lead sleeve 6I which may be closed and secured at its ends 62 around the cable by any appropriate method, for example, soldering.

In cases where telephone cables have a relatively large number of pairs of lines (Fig. 5) a space-saving loading complement of coils 63 may be made up as shown in Figs. 5v and 6 wherein a number of dowel-mounted coil assemblies I9 are placed structurally in parallel and connected into the telephone lines in a cable 64. If all of the lines in the cable are not to be loaded the unloaded lines 65 may be used as la core around which the dowel-mounted vassemblies I9 maybe placed in order to have the compactne'ss resulting from symmetry at the. loading point thereby permitting the loading Aunit to be sheathed with the cable under one cover. In Fig. 5 the loaded telephone lines are indicated at l0. A metal sleeve 'll may be used to enclose the loading complement 63 and the telephone lines atthe loading point. The sleeve 'Il (Fig. 5) and the Isleeve 6l (Fig. 7) may be lined with paper 12 `or another insulating material and thev unused space within the sleeve may be filled with an insulating compound.

What is claimed is: I Y

1. An inductive loading device 'for a cable of telephone wires comprising a toroidal coil, a rod for supporting said coil, a terminal supporting washer mounted on saidrod and adjacent to said coil, said washer having extending therefrom a pair of conductors, one end of each of which is connected to the end of thewindings of said coil and the other end of each of said conductors being relatively-long for connection to a'tele'phone wire of said cable at opposite ends of said coil, an insulating covering around said device, and a cable coveringA for said cable of telephone wiresen'closing said coil to seal said coil in said cable.

2. A loading ccil assembly for a cableof telephone wires ccmprising a supporting rod, a plurality of toroidal coils mounted on said supporting rod, said coils being alternately angularly staggered to minimize, undesirable inductive effects between adjacent cbils, a'terminal supporting washer associated with each coil and having terminals connected tosad coils, saidwasher'also having leads extending ltherefrom lying along and extending from 'the ends of `the assembly. strips of tape on said coils and-undersaid terminals for preventing possible kshort circuits Lbe 5 tween said terminals and said coils, a coating of solvent-type insulating varnish around said assemblage of coils and washers, and a cable covering for said cable of telephone Wires enclosing said assembly.

3. A loading coil assembly for a cable of telephone Wires comprising a supporting rod, a plurality of coil elements mounted on said rod, terminal supporting Washers associated with said coil elements and mounted on said rod, said ter minal supporting Washers having conductors eX- tending therefrom, one end of each of said conductors being relatively short and connected to one of said coil elements and the other end of said conductors being relatively long and lying along said assembly and extending beyond the ends thereof, a coating around said assemblage of coils and Washers of baked solvent-type insulating varnish, a second coating around. said as.

semblage comprising a balzed mixture of a solventn type insulating Varnish and a filler, and a cable covering for said cable of telephone Wires enclosing said assembly.

4. A loading coil assembly for insertion in a covered cable of telephone wires comprising a plurality of toroidal coils having central openings, a rod extending through said openings, a terminal supporting washer associated with each of said coils, said washers being mounted on said rod, terminals carried by Said Washers and connected to said coils, said rod with the coils and Washers thereon forming a cylindrical loading coil unit, leads connected to Said terminals and extending axially in opposite directions along the periphery of the loading coil unit and beyond the ends thereof and connected to telephone wires of said cable at opposite ends of the loading coil unit, an insulating coating on said unit and leads except for portions of the leads extending beyond the ends of said unit, and a cable coj/ering forthe cable of telephone Wires enclosingsaid loading coil unit.

EDWARD J. CRANE.

ROBERT P. CROSS, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED sTATEs PATENTS 

